The present invention relates to a transmission apparatus in a mobile communication system and, more particularly, to a transmission apparatus in a mobile communication system using the CDMA (Code Division Multiple Access) scheme.
As shown in FIG. 9, a transmission apparatus in a conventional cellular mobile communication system comprises pulse shaping filters 201 and 202 for receiving transmission signals S′1 and S′2, respectively, multipliers 203 and 204 for multiplying the outputs from the pulse shaping filters 201 and 202 by carrier waves, an adder 205 for adding the outputs from the multipliers 203 and 204, a transmission amplifier 206 for amplifying the output from the adder 205, a circulator 207 for receiving the output from the transmission amplifier 206, and an antenna 208 for radiating the output from the circulator 207 as a radio wave.
In this arrangement, the transmission signals S′1 and S′2 are limited in their bands by the pulse shaping filters 201 and 202 and multiplied by carrier waves by the multipliers 203 and 204, respectively. The output signals from the multipliers 203 and 204 are added by the adder 205 and then sent from the antenna 208 through the transmission amplifier 206 and circulator 207.
Generally, the transmission power of a mobile communication system is designed to be small outside the band, as shown in FIG. 10. In the above-described conventional transmission apparatus, however, since the power is amplified by the transmission amplifier 206 after bands are limited by the pulse shaping filters 201 and 202, sufficient attenuation is required in bands B1 and B2 outside a band B0 in use. To obtain sufficient attenuation outside the band, the pulse shaping filters 201 and 202 must have steep characteristics or the transmission amplifier 206 must have high linearity.
However, steeper the characteristics on a pulse shaping filter and higher the linearity on a transmission amplifier are required, more the power consumption and the cost are necessary.